Power converters are indispensable devices in electrical platforms and systems such as computing platforms, communication and mobile systems, medical systems, electric vehicles, military systems, renewable energy systems, aerospace systems, and almost all peripherals and devices. These systems and related applications impact people's daily life. A Department of Energy (DOE) Advanced Research Projects Agency-Energy (ARPA-E) workshop of Mar. 2, 2010 concluded that new technology for power electronics and power converters is critical for achieving higher energy efficiency and significant cost reduction and size. The new technology would also promote the United States as a technology leader. Generally, there was agreement at the conference that breakthroughs in power electronics research and technology are critical for reducing energy consumption of these systems by 25-30%. The workshop participants also acknowledged that the use of power electronics circuitries will increase and become a larger part of many systems resulting in improving system energy efficiency by more than 80%.
Power converters convert voltage or current from one level to another and/or from one form to another in order to supply energy to a specific load. Such power converters are of several types, such as DC-DC power converters, AC-DC power converters, DC-AC power inverters, and AC-AC power inverters. Switching DC-DC power converters have the advantage of much higher energy efficiency as compared with converters using linear regulators. However, the switching DC-DC power converter is generally larger than the linear regulator converter primarily because it typically requires power inductors, power transformers, more switching power devices and control circuits. Nonetheless, the switching DC-DC power converters are widely used especially when the energy efficiency is crucial.
In general, the integration and size reduction of other technologies, such as Integrated Circuits (ICs) for microprocessors and other general purpose processors (e.g., graphic ICs and communications ICs), are advancing at a faster pace than switching power converter technologies. Integrating power converters on-chip yields several advantages such as smaller size, lighter weight, reduced distribution, reduced distribution losses, and potentially reduced the EMI (Electromagnetic Interferences).
Magnetic power devices for switching converters include power inductors and power transformers. These magnetic power devices usually occupy more than 30% of the total switching power converter board space and are usually the most difficult components to integrate on-chip. Such integration is particularly difficult with small chips having low power losses and that require high inductance density. Hence, there is a significant inductor technology challenge for on-chip integrated power converters and for System-On-a-Chip (SoC) devices.
When the dimensions of solid materials are reduced to nanometer size, the materials often exhibit new and interesting behavior which can constitute the basis for a new generation of electronic devices. Nano-particles may exhibit unexpected and strange physical and chemical properties compared to conventional or classical materials. For example, copper is a good conductor, while the nano-copper is an insulator. Similarly, nano-magnetic materials have higher density and higher permeability than conventional classical materials. Hence, nanotechnology may help achieve reliable nanometer-scale power devices with small footprints and reduced power consumptions. Consequently, there is a need to develop new nanotechnology-based power devices that can result in transformative advances.
A DC-DC switching power converter typically comprises switching power devices such as MOSFETs (Metal Oxide Field Effect Transistor), an analog and/or digital control circuit, filter capacitors, power inductors, and sometimes power transformers. Switching power devices and control circuits can be easily integrated on a single chip, but the power inductors are often bulky and difficult to integrate with other components. In most cases, power inductors are off-chip components, which typically is an obstacle for reducing the size of switching power converters. Moreover, the power inductor is often one of the largest components in a switching power converter, and it is accountable for much of the weight and the size of a switching power converter. For example, in a DC-DC buck power converter with a 5V-12V input, a 1V output and a 10 W load, the inductor typically makes up more than 30% of the total switching power converter size.
For many electronic systems, it is desirable to develop integrated DC-DC power converters for System on Chip (SoC) applications. The most common approach to integrate power converters include: Power System in Package (PSiP) and Power System on Chip (PSoC). PSiP uses off-shelf power inductors in order to supply large power requirements, but such inductors limit size reduction. PSoC integrates power inductors directly on IC (Integrated Circuit) chips. Such an approach can minimize size by taking advantages of known micro-fabrication technologies. However, the small achievable inductance value (or inductance density) and the low quality factor (high power loss) of inductors fabricated using conventional technologies put constraints on footprint reduction.
Therefore, it appears to be advantageous to replace conventional technology with nanotechnology to achieve reliable nanometer-scale power devices with smaller footprints and less power consumption. Scaling the power inductor to nanometer size helps to reduce converter size. Nanotechnolgy power inductors would provide for high-density on-chip integration of the power converters resulting in optimum power management, lower discrete component count, smaller footprint, lower distribution losses, and lower parasitic delays.